The human brain allows for depth perception through binocular stereopsis, in part, by use of range estimates from a left eye perspective and a right eye perspective. In binocular stereopsis, a viewer's eyes register two images, a left eye image and a right eye image, which are transmitted to the brain for processing. The brain then processes the images to perceive a three-dimensional stereo image. One goal of computer vision and/or computer presentation is to provide a viewer with same or similar perception.
In general, a single computer displayed image cannot effectively provide a viewer with three-dimensional stereo image perception; instead, at least two images must be displayed, e.g., one for each eye. Ultimately, each displayed image should be of a high quality and in a storable and/or a streamable format. However, even in non-stereoscopic video a downward progression exists wherein the resolution, and hence quality, of content distributed to a viewer is much less than that of the original content. For example, a professional digital video camera may acquire image data at a resolution of 1280 pixel by 720 lines, a frame rate of 24 frames per second (fps) and a color depth of 24 bits. The acquisition rate for such content is approximately 530 million bits per second (Mbps); thus, two hours of filming corresponds to almost 4 trillion bits of data (Tb). For viewing, this content must be distributed at approximately 530 Mbps or downloaded as a file having a size of approximately 4 Tb. For stereoscopic viewing, using a scheme that requires video content for a left eye and video content for a right eye, the requirements typically double: an overall bit rate of approximately 1.6 billion bits per second (Gbps) and an overall file size of approximately 8 Tb. At present, bandwidths and recording media commonly used for commercial distribution of digital content cannot handle such requirements. Thus, re-sampling and/or compression need to be applied to reduce the bit rate and/or file size.
Perhaps the most widely used method of compression is specified in the MPEG-2 standard. Products such as digital television (DTV) set top boxes and DVDs are based on the MPEG-2 standard. As an example, consider a DVD player with a single sided DVD disk that can store approximately 38 Gb. To fit the aforementioned 2 hours of video onto this disk, consider first, a re-sampling process that downgrades the video quality to a format having a resolution of 720 pixel by 486 line, a frame rate of approximately 24 fps and a color depth of 16 bits. Now, instead of a bit rate of 530 Mbps and a file size of 4 Tb, the content has a bit rate of approximately 130 Mbps and a file size of approximately 1 Tb. However, for stereoscopic viewing, using a scheme that requires video content for a left eye and video content for a right eye, the requirements typically double: an overall bit rate of approximately 260 Mbps and an overall file size of approximately 2 Tb. To fit this 2 Tb of content on a 38 Gb single sided DVD disk, a compression ratio of approximately 60:1 is required. When storage of audio and sub-titles is desired, an even higher compression ratio, for example, of approximately 70:1, is required. In addition, to decode and playback the 38 Gb of compressed content in 2 hours, an average bit rate of approximately 5 Mbps is required.
In general, MPEG-2 compression ratios are typically confined to somewhere between approximately 8:1 and approximately 30:1, which some have referred to as the MPEG-2 compression “sweet spot”. Further, with MPEG-2, transparency (i.e., no noticeable discrepancies between source video and reconstructed video) occurs only for conservative compression ratios, for example, between approximately 8:1 and approximately 12:1. Of course, such conservative compression ratios are inadequate to allow for storage of the aforementioned 260 Mbps, 2 hour stereoscopic video on a DVD disk. Thus, to achieve a high degree of transparency, source content is often pre-processed (e.g., re-sampled) prior to MPEG-2 compression or lower resolution source content is used, for example, 352 pixel by 480 lines at a frame rate of 24 fps and a color depth of 16 bits (a rate of approximately 64 Mbps). Two hours of such lower resolution content (a file size of approximately 450 Gb) requires a compression ratio of approximately 12:1 to fit a single sided 38 Gb DVD disk. However, for stereoscopic viewing, using a scheme that requires video content for a left eye and video content for a right eye, the requirements typically double: an overall bit rate of approximately 130 Mbps and an overall file size of approximately 900 Gb; thus, a compression ratio of approximately 24:1 is required to fit this stereoscopic content on a 38 Gb DVD disk.
In practice, for a variety of reasons, MPEG-2 compression ratios are typically around 30:1. For example, a reported MPEG-2 rate-based “sweet spot” specifies a bit rate of 2 Mbps for 352 pixel by 480 line and 24 fps content, which reportedly produces an almost NTSC broadcast quality result that is also a “good” substitute for VHS. To achieve a 2 Mbps rate for the 352 pixel by 480 line and 24 fps content requires a compression ratio of approximately 30:1, which again, is outside the conservative compression range. Thus, most commercial applications that rely on MPEG-2 for video have some degree of quality degradation and/or quality limitations. Further, to achieve a 2 Mbps rate for stereoscopic video, using a scheme that requires video content for a left eye and video content for a right eye, a compression ratio of approximately 60:1 is required, which is outside specifications of the reported almost NTSC broadcast quality result that is also a “good” substitute for VHS.
One way to increase video quality involves maintaining a higher resolution (e.g., maintaining more pixels). Another way to increase video quality involves use of better compression algorithms, for example, algorithms that maintain subjective transparency for compression ratios greater than approximately 12:1 and/or achieve VHS quality at compression ratios greater than 30:1. Of course, a combination of both higher resolution and better compression algorithms can be expected to produce the greatest increase in video quality. For example, for an exemplary stereoscopic display scheme that relies on video content for a left eye and video content for a right eye, it would be desirable to maintain as much of the 1280 pixel by 720 line resolution of the aforementioned digital video as possible, if not all of such content (or even higher resolution content); it would also be desirable to fit such content onto a single sided DVD disk or other disk. In addition, it would be desirable to transmit such content in a data stream. Technologies for accomplishing such tasks, as well as other tasks, are presented below.